1. Field of the Invention
The present invention relates to a manufacturing method of an SOI (silicon on insulator) substrate including a semiconductor layer formed of a semiconductor material such as silicon.
Note that semiconductor devices in this specification refer to general devices which can function by utilization of semiconductor characteristics, and electro-optical devices, semiconductor circuits, and electronic appliances are all semiconductor devices.
2. Description of the Related Art
Instead of a bulk silicon wafer, integrated circuits using an SOI (silicon on insulator) substrate in which a thin single-crystalline silicon layer is formed on an insulating layer have been developed. By utilizing characteristics of the thin single-crystalline silicon layer, transistors formed in the integrated circuit can be electrically separated from each other completely. Further, since the fully depleted transistors can be formed, a semiconductor integrated circuit with high added value such as high integration, high speed driving, and low power consumption can be realized.
As a manufacturing method of an SOI substrate, a hydrogen ion implantation separation method in which hydrogen ion implantation and separation are combined is known. In the hydrogen ion implantation separation method, an SOI substrate is manufactured mainly in the following process. Hydrogen ions are implanted into a silicon wafer to form an ion implantation layer including microbubbles at a predetermined depth from the surface. A silicon oxide film is formed by oxidizing another silicon wafer which serves as a base substrate. The silicon wafer into which the hydrogen ions are implanted is bonded to the silicon oxide film of the other silicon wafer, so that the two silicon wafers are bonded. Heat treatment is conducted to separate the wafers at the ion implantation layer. Heat treatment is further conducted to improve bonding force of the silicon layer which is bonded to the base substrate.
A method for manufacturing an SOI substrate by bonding a silicon layer which is separated by the hydrogen ion implantation separation method to a glass substrate is known (Patent Document 1: Japanese Published Patent Application No. H11-097379 and Patent Document 2: Japanese Published Patent Application No. 2005-252244). In Patent Document 1, a separation plane of the silicon layer, which is exposed after the separation, is mechanically polished in order to remove a defective layer formed by ion implantation and steps of several nm to several tens of nm at the separation plane. In Patent Document 2, a Si thin film bonded to a glass substrate is irradiated with laser light to be recrystallized, so that crystal quality of the Si thin film is improved.